In fabrication of semiconductor elements and liquid crystal elements, techniques of forming a finer pattern by lithography have progressed rapidly in recent years. One of the techniques is, for example, use of use of irradiation light having a shorter wavelength.
More recently, a lithographic technique using a KrF eximer laser (wavelength: 248 nm) has been introduced. For further shortening a wavelength of radiation, lithographic techniques using an ArF eximer laser (wavelength: 193 nm) and EUV eximer laser (wavelength: 13 nm) have been studied.
As a resist composition suitably used for forming a finer pattern and shortening the wavelength of irradiation light, for example, a so-called chemical amplification-type resist composition has been proposed. Such a composition includes a polymer and a photoacid generator. The polymer is alkali-soluble when an acid-removable group is removed by action of an acid. Furthermore, development and improvement of such a resist are ongoing.
An acrylate polymer transparent to 193 nm light has attracted attention as a polymer for a chemically-amplified resist used in ArF eximer laser lithography.
For example, Patent Document 1 describes a resist copolymer that is produced from monomers of: (A) a (meth)acrylic acid ester where an alicyclic hydrocarbon group containing a lactone ring is ester-linked; (B) a (meth)acrylic acid ester where a group capable of leaving with an acid is ester-linked; and (C) a (meth)acrylic acid ester where a hydrocarbon group containing a polar substituent or an oxygen-containing heterocyclic group is ester-linked.
For these resist compositions containing a resist copolymer, an important property is the ability to form a good pattern. Such a resist copolymer is generally evaluated through measurements of development characteristics and the like in a prepared resist composition.
A method described in Patent Documents 2 and 3 comprises dissolving a resin containing a resist copolymer in a resist solvent, measuring a dynamic light scattering of the solution, and using the resultant specific parameter to estimate degrees of generation of development defects, variation of pattern dimensions (LER), and in-liquid generation of a foreign substance in a resist composition prepared with the resin.